La palabra del día: Solicitud

Feminine noun. From the Latin sollicitūdo. In Legal and Business Spanish is a letter or document in which something is officially requested, an application form. The verb is solicitar. If you are applying for a job, the expression is rellenar una/la solicitud de trabajo. The same if you are requesting anything from an authority, e.g.: solicitud de exención contributiva, solicitar una exención impositiva.
If you are applying to the university, we use inscribirse en la universidad. Iscribirse infers that the application was accepted, in this case it would be better solicitar la inscripción en la universidad. If the U.K. is joining the EU, the expression is ingresar en la UE. The noun is el ingreso. If you are filling the application form to join a gym or a club, we use inscribirse en un gimnasio/un club. The noun is la inscripción. Please do not use aplicar para el gimnasio, etc., even if you hear it from your Spanish speaking friends. It is not just wrong, it also sounds awful.
Aplicar in Spanish has mainly two meanings 1. to put something on something else or in contact with something else and; 2. to employ, manage or put into practice a knowledge, measure or principle, in order to obtain a certain effect or performance in someone or something. In these cases the noun is la aplicación and the adjective aplicable: ley aplicable: applicable law. dc